This invention relates generally to industrial voltage regulators. More particularly, this invention relates to a method and apparatus for determining the selected tap position of a voltage regulator having a plurality of selectable tap positions.
A step voltage regulator is an autotransformer used to maintain a relatively constant voltage level within a power distribution system. Without the use of such voltage regulators, the voltage level of the system could fluctuate significantly and cause damage to electrically powered equipment. Typically, step voltage regulators include an input voltage which may fluctuate from the desired operating voltage, depending upon the existing load conditions. In order to regulate the output voltage to a more constant output level, a buck/boost winding is serially connected with an output winding on the load side. The buck/boost winding has a series of taps removably connectable to corresponding taps located on a tap changing mechanism. The taps of the buck/boost winding are incrementally located upon the winding to provide discrete, incremental changes in the output winding turns. A reversible motor, responsive to a control signal, drives the tap changing mechanism to the appropriate tap on the buck/boost winding to either increase or decrease the output voltage as needed. A neutral position may also be used, such that the buck/boost winding is disconnected from the output winding.
Operators of industrial electrical power installations having step voltage regulators monitor information on tap positions because of the effect on system operation, maintenance and performance analysis. In addition, certain supplemental functions in the control circuitry may depend on the tap position. One method of determining tap position and tap position changes is through the use of a position sensor, mechanically coupled to a tap changing mechanism. This provides a direct measurement of a tap position and its associated direction of movement. However, the use of mechanical position sensors in this application is a fairly recent trend, and thus many voltage regulators are not so equipped. Without a direct position measurement, therefore, an indirect method of tap position detection is needed.
Previously known methods of indirect tap position sensing include the use of current sensors to detect the energization of the tap changing mechanism motor. A counting mechanism may keep track of the number of xe2x80x9cincreasingxe2x80x9d and xe2x80x9cdecreasingxe2x80x9d voltage tap changes made by the tap changer. However, using this method by itself only provides the operator with information on the relative change in tap position; the exact tap position will remain unknown unless an initial tap position is first determined. One method of initialization known in the prior art is to provide a detecting mechanism for detecting when the tap position reaches the neutral position. Until such time, the exact tap position remains unknown. Furthermore, upon deenergization and reenergization of the power system, the control must again wait until the neutral position is reached before knowing the exact tap position.
It is thus desirable to provide a method and apparatus for determining a voltage regulator tap position while addressing the aforementioned drawbacks and deficiencies.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method for dynamically determining tap position in a step voltage regulator. A present tap position is determined and the applied voltage across a tap changing mechanism is measured. Based upon the applied voltage, a directional change in the tap position is detected. A trigger signal is also generated which is responsive to a detected change in tap position. Finally, a new tap position is calculated based upon the present tap position and the directional change in the tap position, when the trigger signal indicates that a change in tap position has taken place.
In one embodiment, a first voltage is measured across the tap changing mechanism. A second voltage is also measured across the tap changing mechanism, with the first and second voltages being used to indicate a directional change in tap position. In another embodiment, the directional change in tap position is detected by comparing signal phase characteristics between the first voltage and the second voltage.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed descriptions and drawings.